The present invention generally relates to the field of communications systems and, more particularly, to systems wherein mobile stations interact with both public and private radiocommunication systems.
The cellular telephone industry has made phenomenal strides in commercial operations in the United States as well as in the rest of the world. Growth in major metropolitan areas has far exceeded expectations. If this trend continues, it is possible that wireless communication techniques will provide the bulk of telecommunication service in some areas. As a result of this growth and demand, wireless services have become more affordable. In light of recent trend of competitive air time rates, customers may choose to make the cellular phone their only means of personal communication. The popularity of these phones is further enhanced by their ability to be used for other (than voice) forms of transmission and reception, such as facsimile devices and modems.
In its evolution, cellular technology is increasingly expanding into new applications such as wireless PBX and private home base stations such as, for example, cordless systems. It is envisioned that a phone used in public cellular systems will also be used in the workplace and at home, both of which operate on a private system. Unlike public systems which charge for air-time, these private systems typically operate on the basis of a flat or fixed periodic charge. In order to enable cellular phones to connect to private systems without incurring air-time charges, however, owners of portions of the radio spectrum used to support public cellular systems must permit usage of their systems for access to private system. The incentive for these owners is that if users make cellular units their primary form of communication, an increase in usage of cellular phones in the public system will result. This in turn leads to increased revenue to owners of the radio spectrum in which public cellular systems operate.
FIG. 1 represents a block diagram of an exemplary cellular mobile radiotelephone system, including an exemplary base station 110 and mobile station 120, which is used to describe conventional techniques for locating and locking to private radiocommunication systems, as well as novel techniques according to the present invention described below. The base station includes a control and processing unit 130 which is connected to the mobile service switching center, MSC 140, which in turn is connected to, for example, a PSTN (not shown).
The base station 110 handles a plurality of voice channels through a voice channel transceiver 150, which is controlled by the control and processing unit 130. Also, each base station includes a control channel transceiver 160, which may be capable of handling more than one control channel. The control channel transceiver 160 is controlled by the control and processing unit 130. The control channel transceiver 160 broadcasts control information over the control channel of the base station or cell to mobiles locked to that control channel. It will be understood that the transceivers 150 and 160 can be implemented as a single device, like the voice and control transceiver 170 in mobile station 120.
Mobile station 120 receives the information broadcast on a control channel at its voice and control channel transceiver 170. Then, the processing unit 175 evaluates the received control channel information, which can include characteristics of cells that are candidates for the mobile station to lock on to, and determines on which cell the mobile should lock. Once the mobile station has received this information, it can compare its own stored information, e.g., regarding cell preferences, with those transmitted on the control channel, e.g., type of cell and network owner.
The mobile station 120 also includes an input device 185, such as a numeric keypad, which allows a user to interact with the mobile station. A display device 190, such as an LCD screen, provides a visual display of information to the user. In addition to being configured as a cellular telephone, the mobile station may also be a PC card, e.g., a card designed in accordance with the PCMCIA standard, which is connected to a personal computer, e.g., a laptop. In this latter case the display device would be the PC monitor. The mobile station also includes memory 180, which may include various information associated with private radiocommunication systems which the mobile station 120 is authorized to use.
When a mobile station powers on, it will attempt to locate a control channel from which it can, for example, obtain overhead information regarding system operation, receive paging messages and initiate calls. Various techniques are available for locating control channels in public systems, which techniques are typically specified by the applicable radiocommunication standards. An example of techniques by which control channels can be located is found in U.S. Pat. No. 5,570,467, the disclosure of which is incorporated here by reference.
In order for a cellular mobile unit to operate in a private system, it has to locate a control channel of the private system. When a user is located in the vicinity of a private system, it is desirable that the user""s cellular mobile unit will lock onto the private system instead of the public system to reduce or eliminate the air-time charges mentioned above.
In addition to techniques for locating control channels associated with public systems, there are also exiting methods available for enabling mobile units to detect the presence of a nearby private system, e.g., the method specified in the TIA/EIA 136 standard. However, this method depends on the mobile unit detecting certain characteristics of a public system in which a particular private system is located. The mobile unit may, for example, have stored in its memory, certain identifying characteristics of particular public cells such as system and cell identity. Whenever the mobile unit is locked onto the public cell that matches the stored characteristics, the mobile unit may enter a control channel search algorithm for an associated private system.
According to another method, the mobile unit simply searches periodically for a private system. That is, the mobile unit periodically attempts to locate a control channel having a particular private system identity without reference to any particular public cell.
These existing methods, however, have certain disadvantages. Under the first method described above, if the operator of a public system changes the cell layout by introducing more cells, the mobile unit will not detect the stored characteristics of the public cell in which a private system is located. Thus the memory contents of the mobile unit must be updated, for example, by a user, in order to account for changes in the public system made by the operator so that the private system can still be reached. With the periodic search method, the mobile unit, by having to search constantly, drains its battery. Moreover, the mobile unit is unable to detect incoming pages on the public system while it searches for control channels of the private system. What is needed, therefore, is a more effective method for a mobile unit to detect the presence of a private system and locate control channels associated therewith.
According to exemplary embodiments of the present invention, a mobile station can include a proximity detector which informs the mobile station when it is near a proximity system. The proximity system can be integrated into the private radiocommunication system or can be a standalone system that is connected to the private radiocommunication system. The proximity system can emit a signal with or without data modulated thereon for detection by the mobile station. According to other exemplary embodiments of the present invention, the proximity system can employ techniques which permit more sophisticated, two-way data transfer.
If the proximity system simply informs the mobile station of its presence, then the mobile station can institute a search for a control channel associated with the private radiocommunication system. If, on the other hand, the proximity system is able to also transfer information to the mobile station, e.g., regarding the private radiocommunication""s control channel frequency (or a subset of frequencies within which the control channel can be found), this can aid the mobile station in locking onto the private radiocommunication system.
According to further exemplary embodiments of the present invention, the proximity device in the mobile station can be implemented in a number of different ways, e.g., as a radio frequency (RF) sensor, a magnetic sensor or a more sophisticated, short range receiver, and provides a trigger for the mobile station to attempt to connect to the private radiocommunication system. If the proximity detection techniques employed provide the additional capability for the proximity system to convey information other than a mere proximity signal, the mobile station can then be configured to receive and output such information. For example, the proximity system system could convey the user""s e-mail or voicemail along with the proximity signal. Analogously, the mobile system can also be configured to upload information to the proximity system.
According to still other exemplary embodiments of the present invention, systems and methods provide access control to, for example, doors, buildings, etc. by authenticating the mobile station""s identity and selectively providing access based on the authentication process. Authentication can be conducted between the mobile station and any one of the proximity system, the private radiocommunication system and the public radiocommunication system.